42 Macarpineの合成 : 異常Bischler-Napieralski反応によるAzoniaazulene骨格の形成(口頭発表の部)

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In the course of synthetic studies on benzo[c]phenanthridine alkaloids for their structure-activity relationship macarpine (1), a fully aromatized one carrying six oxygen functions, was synthesized as shown in Scheme 1. In the synthesis we succeeded in regioselective introduction of a nitrogen function into the para position of a hydroxyl group in a naphthol (9) by newly developed SE reaction under basic condition (basic nitrosation). Bischler-Napieralski (B. N.) reaction has been used for the construction of isoquinoline skeleton in our synthetic strategy. Treatment of a naphthylformamide (12) with POCl_3 followed by NaBH_4 reduction afforded dihydromacarpine (13), which could be easily converted into 1, along with an undefined product (14). The corresponded product (17) to 14 was also obtained in the reactions using a naphthylformamide (15). (Scheme 2) The unexpected benz[g]indole structure fused to oxabicyclooctene system for 17 was unambiguously established by X-ray crystallographic analysis. (Fig.1) Thus, it could be reasonable to deduce a benz[g]indole structure for 14 . Fractional recrystallization of the B. N. products of 15 from methanol allowed us to isolate an anomalous cyclized product of the azoniaazulene derivative (19), easily reducible to a benz[g]indole (17), in addition to a normal cyclized product (18). The structure of 19 was determined by its spectral data including NOE (Fig. 2) and COLOC (Fig. 3) experiments. Formation of an azoniaazulene (20) was also found in the B. N. reaction of 12 (Scheme 3) Interestingly, normal cyclization was observed in the B. N. reactions of 21 (R=Me or ^iPr) in which a methylenedioxy group in the 2-aryl substituent was replaced by methoxy groups. On the other hand, a corresponding phenolic 21 (R=H) caused abnormal B. N. reaction. (Scheme 4)
天然有機化合物討論会の論文
1994-09-20

42 Macarpineの合成 : 異常Bischler-Napieralski反応によるAzoniaazulene骨格の形成(口頭発表の部)

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